Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $59.98   7.461%   $64.4551   $64.46   $64.45   $64.50  
  Purchase #2 $143.66   6.774%   $153.3915   $153.39   $153.40   $153.40  
  Purchase #3 $23.63   3.727%   $24.5107   $24.51   $24.50   $24.50  
  Purchase #4 $216.52   7.379%   $232.497   $232.50   $232.50   $232.50  
  Purchase #5 $235.71   6.151%   $250.2085   $250.21   $250.20   $250.20  
  Purchase #6 $212.68   6.142%   $225.7428   $225.74   $225.75   $225.70  
  Purchase #7 $241.81   3.481%   $250.2274   $250.23   $250.25   $250.20  
  7 purchase totals = $1,133.99       $1,201.0330   $1,201.04   $1,201.05   $1,201.00